The present invention relates to a flexible container for the transportation and storage of bulk material, especially free-flowing pulverulent or granular material. The invention also relates to a method for manufacturing such flexible container.
Today there are several known types of containers for transportation of free-flowing bulk material. Some are of the one-trip type and others are intended to be used several times. Such containers are usually called Intermediate Bulk Containers.
Swedish patent application Ser. No. 7405935 describes a flexible container which can be lifted when filled. This container is provided with a special lifting device which comprises a rope, one end of which is secured to the container top. The other end of the rope runs through the center of the container and is secured at the container bottom, for instance to a plate below the container bottom. In this way the stress is better distributed when the container is lifted. Although this lifting device distributes the stress somewhat better than do conventional flexible containers, its construction is rather complicated, thus increasing the cost of manufacturing the container. Another drawback is that the container is made of a number of different components, and the total quantity of material per container is large.
Further, Danish Pat. No. 132,877 describes a flexible container having a squarish bottom section with a discharge opening that is covered by a loose piece of material. This piece is cut before discharging. Before refilling the container, a new cover-piece is placed in it. The container is equipped with four specially fastened lifting loops, and its upper section has a special lid with a filling opening that can be closed. This rather complicated container which consists of several components that have to be joined together, requires a complicated and thus expensive manufacturing apparatus, and accordingly the cost of the container is made expensive. Such a container is consequently intended to be used several times. The four separately fastened loops result in an uneven distribution of the vertical stresses in the container's fabric which thus must be made from strong and expensive material.
The present invention is the result of further development of the flexible container according to Norwegian patent application No. 4350/73, corresponding to British Pat. No. 1,475,019. This container is made from a single piece of material that is folded and sewn together along its sides and bottom. Approximately at the middle of the folded edge there is a slit which constitutes the filling opening of the container. The side seams terminate some distance from the folded edge thus providing to lifting loops which extend from the slit to the point of intersection between the imaginary extension lines of the side seams and the folded edge.
The container has proved to be well suited for transportation of bulk material. It is cheap and can therefore be used as a one-trip container. However, by destructive, dynamic testing it has been found that the stress distribution during lifting of the container is not optimal due to the design of the bottom of the container.